1. Field of the Invention
The present invention relates to a data storage apparatus, a data processing method, a recording medium, and a program in which security of data can be ensured.
2. Description of the Related Art
In recent years, a large amount of information is transmitted/received through a transmission line such as the Internet or various recording media in everyday life due to development of an information processing technology. In such transmission/reception of information, cryptography is used to ensure security.
Secret key cryptography is an example of the cryptography. In the secret key cryptography, a transmitter and a receiver have a common secret key. The transmitter transmits data encrypted by using the secret key and the receiver decrypts the encrypted data by using the secret key.
As an example of cryptography using a secret key method, a method for performing mutual authentication between a transmitter and a receiver by using two types of secret keys has been proposed (e.g., see Patent Document 1: Japanese Unexamined Patent Application Publication No. 10-20780).
On the other hand, public key cryptography, which replaces the secret key cryptography, has become common. In the public key cryptography, data is encrypted and decrypted by using a pair of keys. One of the two keys serves as a public key and is widely open to the public and the other serves as a secret key and is strictly managed by a person who released the public key. Data encrypted by the secret key can only be decrypted by using the public key as a counterpart, and data encrypted by the public key can only be decrypted by using the secret key as a counterpart. In this method, data encrypted by using the public key cannot be decrypted until a person who has the secret key obtains it, and thus the data can be securely transmitted. In the secret key cryptography, a secret key needs to be transmitted to a receiver of data through a safe line so that a third party cannot obtain the key. On the other hand, in the public key cryptography, the safety of a line to transmit a public key need not be strictly managed and thus its holder can easily manage the key without caring about theft of the key.
For example, a public key infrastructure (PKI) is known as a security infrastructure using public key cryptography.